A silicone-based synthetic oil has heretofore been used as a lubricant for use at high temperature, and it has been verified that its evaporation loss at high temperatures is small. Conventional silicone-based synthetic oils, however, have disadvantages in that their load-carrying capacity is seriously low and they lack characteristics such as detergency which are required for the lubricant. In order to overcome the above-described problems and further to give other characteristics, it has been attempted to add various additives for lubrication, but with limited success since the additives are not soluble in the silicon-based synthetic oils. Hence they are not suitable for practical use.
For lubricants being used in an engine of the adiabatic type, a super high-temperature gas turbine bearing, an engine with a turbo charger, and so forth are required to withstand temperatures as high as 200.degree. C. or more, although the upper temperature limit of the conventional lubricants for high-temperature use is 170.degree.-180.degree. C.